1. Field of the Invention
The present invention relates generally to a vibration mitigation device for a nuclear reactor component, and to a method of mitigating vibration in a nuclear component.
2. Description of the Related Art
Boiling water reactors (BWRs) have emerged as a reliable type of nuclear reactor for producing electrical energy. However, some BWRs have experienced cracking in various components of the BWR. One contributing factor to component cracking in a BWR may be due to high cycle fatigue. Typically, a BWR may operate from about one to two years on a single core loading of fuel. Upon completion of a given period (known as an energy cycle or fuel cycle), approximately ¼ to ½ of the least reactive fuel (oldest or most burnt) may be discharged from the reactor. The number of cycles which may constitute a substantially high number of cycles may vary from BWR to BWR, as other factors may affect cycle time, such as design, operating conditions, etc.
High cycle fatigue may be caused, for example, by a substantially high acoustic frequency vibration, for example a frequency above 100 Hz, and/or a substantially low acoustic frequency vibration, for example a frequency below 100 Hz. It should be understood that the frequency which constitutes a high and/or a low acoustic frequency may vary based on the application. The amplitude of a vibration in a BWR may directly influence or exacerbate high cycle fatigue, which in turn may cause the cracking of a component of the BWR. The amplitude of the vibration in the BWR experienced by a component of the BWR may be directly proportional to the stress in the component. High amplitude of the vibration in the BWR may lead to a high stress level, which may cause the cracking of a component of the BWR.
FIG. 1 is a cut-away to illustrate an upper portion of a conventional reactor pressure vessel (RPV) of a BWR. Typically, and referring to FIG. 1, a BWR may include an upstanding reactor pressure vessel 10 which incorporates a lower reactor core structure beneath which are control rod drive mechanisms (not shown for clarity). Above the core may be a steam separator assembly 25 and a steam dryer assembly 30 leading to a steam outlet 35. One or more reactor components of the steam separator assembly 25 or steam dryer assembly 30 may experience vibration due to increased vibration amplitude due to the stresses from the aforementioned high cycle fatigue. This may accelerate cracking of the reactor component.